High-frequency radiant energy apparatus



March 9, l948- G. L. TAwNEY i HIGH FREQUENCY RADIANT ENERGY APPARATUSFiled July 19, 1944 5 sheets-sheet s' COMBINING CCT COMBINING CCT IINVENTOR GERELD I .TAwNEY VLM March 9, 1948.

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G. L. TAWNEY HIGH FREQUENCY RADIANT ENERGY APPARATUS Fil ed July 19,1944 5 Sheets-Sheet 4 @E REL!) L TAWNEY ATTORNEY Mama 9, 1948. TAWNEY2,437,281

HIGH FREQUENCY RADIANT ENERGY APPARATUS Filed July 19, 1944 5sheets-sheet 5 xNvENT'oR GERELD L.TAwNEY A'I'I'ORNEY Patented Mar.9,1948

HIGH-FREQUENCY RADIAN T ENERGY APPARATUS Gerold Leon Tawney, Hempstead,N. Y., assignor to The Sperry Corporation, a corporation of DelawareApplication July 19, 1944, Serial No. 545,580

(Cl. Z50-11) 22 Claims. l

The present invention is concerned with the art including antennas forthe radiation or reception f radiant energy, such as electromagneticWaves, and is more particularly concerned with highly directionalantenna apparatus having a periodically varying direction of maximumdirectivity.

In many useful applications of electromagnetic energy, and especially inthe ultra high frequency eld, it is desirable to continuously andperiodically sweep or scan the directivity char--4 acteristic of ahighly directive antenna system according to a predetermined law or ruleof variation. Such apparatus may be used for sweeping a radiated beam ofradiant electromagnetic energy according to a predetermined pattern, orfor successively and continuously receiving radlant energy in selectivefashion from periodically varying portions of space. Such apparatus hascome to be known as a scannen In the prior art it has been known to formsuch scanning apparatus by physically and mechanically moving adirective antenna system so as to cause its directivity characteristicto vary in accordance with the desired pattern. Such systems, Whileeffective for many purposes, are complicated by the necessity forproviding mechanical moving parts and motive means for such movingparts. Also, such systems are limited in rates or periodicity ofscanning, since the antenna is positioned by mechanical means whichpermit only relatively low scanning rates or frequencies. It is,therefore, highly desirable to provide scanning systems in which movingparts are completely eliminated and which are adapted for scanning ratesor frequencies higher than those attainable with mechanical scanners.Such inertialess stationary scanners have been termed electronicscanners and it is an object of the present invention to provideimproved and novel electronic scanners for these purposes.

According to the present invention, electronic scanning may be performedby providing a plurality of diierent antennas having directivitycharacteristics covering diierent portions of. space, and which are`preferably overlapping in space, these antennas being successivelyenergized by, or rendered receptive to, electromagnetic energy, toprovide scanning action.

According to one aspect of the present inven. tion, the energy to beradiated is supplied successively and only partially concurrently tosuccessive antennas, having different overlapping directivitycharacteristics. Similarly, for a receiving scanner, energy is takensuccessively and only partially concurrently from successive antennashaving overlapping directivity characteristics. As a renement on thissystem, the wave form of the energy radiated to or taken from theantennas is selected to provide a substan-` tially smooth and continuoustransfer of energy to or receptivity from, the successive antennas.

According to another aspect of the invention, in a radiating scanner,these Wave forms are produced by the synthesis of suitably relatedconstant single'frequency waves, whose amplitudes and phase relationsare adjusted or selected in accordance with the invention to provide therespective plurality of diierent waves to be radiated by the respectiveantennas.

According to another aspect of the invention, the electronic scanningfor radiation is effected by separately radiating single constantfrequency Waves of suitably related frequency, each such Wave beingradiated to essentially the same portion of space, b-ut with anindividual respective directivity characteristic, the phases anddirectivity characteristics of these several single fre quency Wavesbeing adjusted or selected in accordance with the principles of thepresent invention to provide electronic scanning as desired.

Accordingly, it is an object of the present invention to provideimproved methods and apparatus for effecting electronic Scanning.

It is another object of the present invention to provide improvedmethods for varying the directivity characteristic of an electromagneticdirectional antenna `to scan a desired field of view without the use ofmoving parts, and at high rates substantially without inertia.

It is a further object of the present invention to provide improvedmethods and apparatus for producing electronic scanning by use of anelectromagnetic antenna of varying directivity characteristic, saidantenna radiating several waves of the same wave form with diirerentdirectivity characteristics and into different portions of space.

It is still another object of the present invention to provide improvedmethods and apparatus for producing electronic scanning by radiating aplurality of single frequency waves to the same portion of space withrespectively individual directivity characteristics.

Other objects and advantages will become apparent from thespecification, taken in connection with the accompanying drawingswherein,

Fig. 1 is a diagram illustrating a plurality of highly directive lobesof electromagnetic radiation having overlapping directive characteristicpatterns but with respectively different axes of maximum directivity;

Fig. 2 shows a series of time graphs of modulated electromagnetic vvavesto be radiated or received in accordance with the characteristics ofFig. 1 to produce the advantages of the present invention;

Fig, 3 shows a Vset of time graphs similar to, but modiiied with respectto Fig. 2;

Fig. 4 shows` a perspective view partially cut 3 away of a reflector andwave guide feeds therefor for producing the characteristics of Fig. 1;

Fig. 5 shows a set of time graphs similar to Fig. 2;

Fig. 6 shows a schematic wiring diagram of a system for producing thewaves to be radiated in accordance with the characteristics of Fig. 1;

Fig. 7 shows a schematic wiring diagram of a system similar to Fig. 6;

Fig. 8 shows a' further schematic wiring diagram of a system similar toFigs. 6 and 7;

Fig. 9 shows a diagram useful in .explaining certain principles of thepresent invention;

Fig. 10 shows a schematic wiring diagram of a system operating inaccordance with the principles illustrated by Fig. 9;

Fig. 11 is a graph of a desired directivity-characteristic showing thepeak electric intensity as a function of angular deviation from the axisof maximum intensity;

Fig. 12 shows a curve of electric intensity as a function of position inthe mouth of a radiator corresponding to the characteristic of Fig. 11;

Fig. 13 shows curves of the amplitude of various Bessel functionsplottedY against position in the mouth of the radiator;

Fig. 14 shows curves of the amplitude of the several components of wavesto be radiated, plotted against position in the mouth of the radiator;

Figs. 15, 15A and 16 are diagrammatic representations of antennassuitable for producing some of the necessary characteristics of theinvention; and

Figs. 17 to 19 are curves similar to Figs. 12 .to -14 relating to adifferent required directivity characteristic.

Fig. 1 shows a number of highly directive radiation or directivitypatterns II, I2, I3, I4 and I5, whose respective axes of maximumdirectivity I6, I1, I8, I9 and 20 are disposed at slight angles to oneanother as shown. These patterns may be produced by independentdirective antennas or in the manner discussed more in detail below.

One type of scanning of the radiation from such an antenna system can beobtained by successively and intermittently supplying the high frequencyenergy to be radiated to the respective antennas producing theseradiation patterns II to I5. This is illustrated in Fig. 2 wherein areshown the wave forms or time graphs of the waves radiated in accordancewith the respective patterns, under these conditions. Thus, in Fig. 2,lcurve A represents the wave form of the wave transmitted in accordancewith 'pattern II. Curves B, C, D, and E similarly show the wave forms ofthe waves radiated according to patterns I2 to I5, respectively. Thesewaves have a carrier frequency f and each will be seen to have anenvelope which is -a periodic pulse wave having a pulse repetitionfrequency fo `and .a pulse duration T. The successive envelopes of thewaves of Fig. 2 are time-shifted with respect to one another by anamount a between successiveenvelopes, a being equal to (which is alsopreferably the value of T) where n is the number of separate wavesradiated, corresponding to the number of radiation patterns utilized,and illustrated here as iive in number. Any desired number may be used,Adepending on the desired range and relative smoothness of the Scanning-In this manner, by radiating high frequency energy in accordance withthe respective radiation patterns I I to I5, the energy radiated beingas shown in Fig. 2, the resultant radiated energy will stepdiscontinuously and progressively from direction I6 toward direction 2i)and then will repeat this `operation successively. This is a type ofscanning which may be useful under some circumstances, but is generallytoo crude because of Vits discontinuous character.

This type of scanning has the further disadvantage that a very largenumber of side band frequencies will be required. Thus, as is wellknown, a square pulse such as the envelope in Fig. 2A can be representedby a Fourier series of the following type:

and will be seen to have an infinite number of components of diierentfrequencies spaced by the amount fo and having a gradually decreasingamplitude, the maximum amplitude of any component being inverselyproportional to the order m of that component. When such a wave ,ismodulated upon a high frequencyV carrier, it

produces a correspondingly infinite number of side band frequencies bothabove and below the carrier frequency. As a practical matter, side bandcomponents having an amplitude factor of less than 5% of the amplitudeof either the carrier. component or the first side band component may beignored. However, even with this practical limitation on `the number ofside bands, an excessively broad band width is required by this system.vTo avoid these disadvantages, the pulse wave envelope of Fig. -2 may bereplaced by the envelope shown in Fig. 3, which represents avdiscontinuous squared-cosine pulse wave; that is, the wave shape of anyone pulse is one complete cycle of the square of a cosine wave ofquarter-period T, these pulses recurring at a repetition frequency fo.It is to be understood that the envelope o f Fig. 3A may be used for thewave radiated by pattern Il, similar squared-cosine pulse waves such asthat in Fig. 3B, time-displaced by the amount a defined above beingutilized for the waves radiated according to the remaining radiationpatterns I2 to I5.

By the use of such a squared-cosine pulse wave instead ofthe squarepulse wave, the number of side band components is greatly reducedbecause the higher order Fourier components of such a squared-cosinepulse wave decrease in amplitude Vas the cube of the component orderinstead of being inversely proportional tothe rst power of the-component order as in the envelope of the wave of Fig. 2. This will beseen from the following expression for these Fourier components.

`the waves of jFig. 2, will'now shift more continuously from -16 to I1,etc., as the energy radiated according to pattern Il decreases and thataccording to pattern l2 increases, in accordance with the envelopes ofthe waves in Figs. 3A and 3B.

In Figs. 1-3 it has been assumed, for illustrative p purposes only, thatfive waves are radiated to produce the scanning. Of course, any numberof suchwaves may be used, ldepending on the range and relativesmoothness of scanning desired.

One convenient and simple way of radiating these plurality of waves isillustrated in Fig. 4. As shown here, a plurality of high frequency waveguides 5l to 55 are provided, each energized by a respective one of thefive waves illustrated in Fie. 2 or Fig. 3. These ive wave guides areplaced in line in front of a preferably parabolic reflector 28 which,for example, may be formed as a parabolic cylinder having relativelyshort axial length, but with an opening across its mouth which ispreferably many times the free space wave length of the radiated wave.By making the central wave guide 53 extend along the focal line or axisof the parabolic reflector, its directivity axis (corresponding to I8 ofFig. 1) will extend along this Afocal axis. The otherV wave guides willthen radiate energy in cooperation with the reflector 28 in directionsslightly angularly disposed with respect to this focal line, and willproduce the plurality l of radiation patterns lli-2li shown in Fig. 1.Other means for separately radiating the several be used in place ofthat shown in Fig. 4.

As will be clear, the type of scanning thus far described is essentiallyunidirectional, that is, the directional beam is swept in a singledirection, returning abruptly and discontinuously to its originaldirection at the end of each scan. If desired, thewave forms shown inFig. 5 can be utilized, which would provide a two-directional scan. ThecurVes'A and E of Fig. 5 have pulse repetition frequencies yof f=(2nl)T. Curves B, C and D are formed by adding two waves of the form of curveA or E, with proper phase shift. Preferably here also, squared-cosinepulses are used in place of the square pulses shown, although the squarepulses may be used where expedient. s

On the other hand, if a conical type of scan is desired, the wave guides5| to 55 may be disposed about an imaginary cylinder whose axiscoincides with the focal axis of a paraboloid of revolution.

yIn this manner the directional beam will have its major directivityVaxis, such as I6, sweep in a substantially conical manner which isuseful for many applications. l

Thus far, nothing has been said about how the waves to be radiated maybe generated. Such waves with respectively diierent directivities mayThe resultant wave to be radiated according to each of the radiationpatterns can then be formed by synthesizing various constant frequencywaves, each having a frequency corresponding to one side band frequency,and being of a constant amplitude equal to the required amplitude bm ofthe side band component. Thus, in Fig. 6, assuming that p side bandcomponents are required in practice, 2p+1 frequency generators 2i areutilized, each producing one of the frequencies fimfn, where m is theorder of the side band and takes any value from 0 (for the carriercomponent) to p (for the pth order side band component). Each of thesewaves is then passed through a respective attenuator or amplifier orother amplitude adjuster, adjusted or selected to produce the amplitudevalue indicated by bm in Equation 3 above. All of these adjusted wavesare then combined in a suitable combining circuit 23 whose output waveNo. 1 will then represent the Wave which, for example, is to be radiatedin accordance with pattern Il.

As shown above with respect to Fig, 2B, the wave to be radiated inaccordance with pattern l2 must be time-displaced with respect to thewave No. 1 by the amount a, where a is a period ofV time equal to nf()Where d is the periodicity of the pulse wave, such as shown in Fig. 2.In order to time displace the complete modulated wave output fromcircuit 23 by an amount a, it can be shown that it is necessary to phaseshift the carrier component of frequency this wave.

f by zero, and to phase shift each side band cornponent to order m by anamount are phase-shifted in leading sense and lower side band componentsare phase-shifted in the op- Vposite sense. That is, the upper side bandcomponents of Wave No. 2 are caused to lead their correspondingcomponents of wave No. l in phase by amount m, and the lower side bandcomponents will then be caused to lag their corresponding components ofwave No. 1 in phase by m. Such phase shifting is performed in respectivephase Shifters 24, whose outputs are then fed to similar amplitudeadjusters 22 and are combined in a combining circuit 23 to form waveNo.2. Similarly, the 21H-1 waves from generators or sources 2| aresupplied to other groups of phase Shifters and attenuators. Each phaseshifter group will produce a time shift of a for its combined outputwave with respect to the preceding Wave, and in this way all the m wavesof Fig. 2 (indicated as five in number in the present illustration), maybe generated. These output time shifted waves may then be radiated as inFig, 4.

Other wave forms, such as in Fig. 3, may be generated by suitableadjustment of the attenuators f or amplitude adjusters 22. Thus, for thesquaredcosine pulse wave, one radiated wave will have the form ofEquation 3, but with Therefore it is merely necessary to adjust theamplitude adjusters 22 to produce outradiated may be synthesized or Fig,6. It is to 'be noted that in the system of Fig.

6 the amplitude of a particular side band component of one of thecombined output waves is .the same as the amplitude of the same sideband component of each of the other output waves: that is,

the amplitude of, for example, the third order side band of wave No` 1is the same as the amplitude of the third order side |band of all theother waves, and both upper and lower'side band .components of the sameorder have equal amplitude. For this lreas-on only one -set of amplitudeadjusters is really necessary, provided that any attenuation which mayexist in the'phase Shifters is equalized. This feature is takenadvantage of in the system of Fig. 7. Here the respective constantfrequency waves derived from sources 2i are.

passed through the respective attenuators or amplitude adjusters 22wherein their amplitudes are adjusted to the values required by theparticular type of combined wave to be produced, taking into account anyattenuation later produced in the circuit.

The system of Fig. 7 also utilizes simplified phase Shifters which havethe form of high frequency conductors such as concentric lines or waveguides. Such conductors have the propertyof substantially constant phaseshift per unit length, which may be designed so that practicable lengthsof conductor will produce the required phase shift Thus, in Fig. 7 theoutputs of attenuators 22.are fed to the phase-shifting energyconductors 3i along which the energy is made to HOW. The outputs ofattenuators 22 are also connected directly by suitable conductors 32designed to have substantially equal phase shifts to the combiningcircuit 23 whose output is then wave No, 1, in the same manner as inFig. 6.

In order to get the time-shifted Wave No. 2, its combining circuit 23 issupplied with energy from the conductors 3l, through leads33, alsodesigned to have substantially equal phase shifts. Energy at the carrierfrequency f is tapped from its corresponding line 3l at a point 35,separated from the corresponding attenuator 22 'by a distance adapted togive a phase shift of some muitiple of 360 degrees. The other taps vfromconductors 3| are located at differing distances from theircorresponding attenuators so that each-side band of order m has a phaseshift of m with respect to the carrier frequency wave, the upper sideband components having leading phase shift, and the lower side bandcomponentshaving lagging phase shift. f

Similarly, the combining circuit '23 producing wave No. 3 has itscarrier frequency component tapped from line '3| at point 36 located togive a phase shift of a multiple of 360 degrees from poi-nt 35. Theother taps from conductors.3i,.connected to combining circuit 23 byleads 3.4 z'ha-ying substantially equal phase shifts, are at.differingdis-` tances from their .attenuatora selected so that therequired phase shifts of 'm are' obtained, m being again the .orderlofthe side band under consideration. In this way a'iillthe waves to bebuilt up from their single frequency components.

It is to be noted that all the conductors '3l need not produce the samephase shift per unit length.

18 For economy of space and -materiaL'those which requiregreatest phaseshift (such as the uppermost one in Fig. 7) may be designed to producegreater phase shift per unit length, to reduce the over-all lengthneeded.

One manner in which the various single frequencies may be produced isalso shown in Fig. 7.

Here, a suitable carrier frequency generator y6| producing frequency fis connected to a mixer 6.3 preferably of the square law type to whichis also supplied a wave of frequency fo from pulse generator 52. Theoutput from mixer 63 will contain many side frequencies fi-pfo, whichmay be separated by suitable iilters 64.

Another phase shifting arrangement similar to that of Fig. 7 is shown inFig. 8, in which the conductors 3| corresponding to 3l of Fig. '7 arebent in the form of semi-circles. Each semicircle 3i' has both ends fedby the two side band components of the same order, that is, by the upperand lower side band of a given order. Thus, the innermost semicircularconductor 3l is supplied with energy of frequency f-l-u at one end andf--fo at the other end, both of these input waves being previouslyadjusted to the amplitude required by the particular type of pulse waveutilized, by amplitude adjusters 22. The second semi-circular conductor3i is supplied with energy of frequency -l-Zfo and f-Zfo at itsrespective ends, properly adjusted in amplitude. The remainingconductors are similarly supplied. Each semi-circle 3i' is designed togive the same phase shift per unit length, and the radii of thesemi-circles are chosen to be in integral multiple relationship, thatis, the second semi-circle has twice the radius of the first, the thirdthree times the first, etc. In this way the lengths and therefore thephase shifts of the several conductors 3i' running between two xed radiiwill vary in integral multiple relationship. 1

A conductor 4|, having predetermined phase shift taps off energy fromeach of the semi-circles 3| for example, at their centers, and isconnected directly to the carrier component source of frequency fthrough the amplitude adjuster 22. The energies at the severalfrequencies fed to this conductor 4| may be arbitrarily considered tohave zero phase. A conductor 4'2 having phase shift substantially equalto that of conductor 4| also taps off energy from the semi-circles alonga radius making an angle 'Y with that of the tap 39. It,will be seenthat the phase of the carrier component of frequency f 4in conductor 42will be the same as in conductor 4|, since the carrier component is feddirectly into both 4i and 42. Energy of frequency f-i-fo in conductor 42will lead that in conductor lil' by the phase shift corresponding to anangle 7 of the rst semi-circular conductor 3|', which is designed orselected to v will then be since the length of arc of the secondconductor 3| vis twice that in the rst conductor 3l', Correspondinglythe phase shift at frequency f-fo will be a lagging phase shift of theamount etc. Other radial conductors 39, 40, 43 similar to 4l, 42 andhaving phase shifts equal thereto are angularly spaced at the angle 'Yand provideV the other waves to be radiated. By this arrangement everyside band component of the Wave to be synthesized will have its properphase shift. If desired, separate amplifying or buier stages may beinserted between the respective taps of each conductor 35 to 63, inorder to compensate for any stray difference in phase shift which mayoccur, and to provide the proper resultant relationships. The combinedoutput waves are derived directly in conductors 39 to t3, Vand may besupplied for example, to the radiating arrangement of Fig. 4.

vEach of the arrangements discussed above has been described withrespectto a radiating scanner. However, they are readily adapted tooperate as receiving scanners. Thus, for a receiving scanner, energyreceived by an antenna similar to that shown in Fig. 4 will betransmitted by guides 5| to 55 to a receiver apparatus. The transmissiondown these guides 5I to 54 is then blocked, in any well-known manner,such as by blocking amplifiers, except at the times and to the extentindicated by the respective pulse Waves of Fig. 2 or Fig. 3.

If signal intelligence is transmitted, the blocking may be done afterindependent detection of the several waves in guides 5| to 55.

The system shown in Fig. 6 may be used as a. receiver scanner byreplacing the generators `2| by corresponding sharply tuned passfilters, and connecting the outputs of these filters to a suitablecombining circuit to which the receiver is connected. In such case, thephase Shifters 2li, circuits 23, and adjusters 22 should be bilateral incharacter, or reversed in connection, to permit transmission fromantenna to receivers.

In Figs. 7 and 8, receiving scanning may be obtained by replacing mixerS3 by a receiver circuit.

In each case, the receiving scanners of Figs. 6, 7 and 8 will have thesame amplitude adjustments and phase shifts as discussed for thecorresponding radiating scanners.

In place of separately synthesizing each ofthe separate waves to beradiated in respectively dif? ferent directions in the manner discussedabove, the present ,invention may be further simplified while stillproducing the scanning without the use of moving parts. This is done byseparately radiating each fixed frequency side band component with itsown directivity characteristic rather than combining the side bands intoseveral different waves which are then separately directively radiatedin different directions.

Thus, referring to Fig. 9, there is shown a schematic diagram which willbe useful in ex-v plaining the operation of this aspect of the presentinvention. In this gure there is shown a directional antenna of suitabletype which, for example, may include a suitably energized parabolicreflector ll. The directivity of this antenna is to be determined toproduce the desired scanning.

First the directivity characteristic to be scanned is chosen, Thischaracteristic is the peak radiation i-leld intensity EM as a functionof angular deviation e from a direction OA of maximum radiation, and isexpressed as Ema). Ii.

the axis OA is at an angle (i: from the focal axis 0K of radiator 5l,then e=0, where 0 is the angle from GX to the direction makingan angle ewith respect to OA,-at which angle 0 there is the eld intensity EM. Theldesired field space pattern is thus expressed by Emea- 11) Y r .Y 1'0 Tomake this pattern scan without altering its shape, it is merelynecessary to vary Thus, if Y pM is the' maximum deviation of OA from OX,and if FM) represents the desired variation of the angular position ofOA as a function `of time t, then =MF(t) and Y where the last factordenotes the alternating character of the field intensity E at thefrequency and EM indicates the maximum amplitude of E during each cycleof frequency which value EM varies with` angular deviation 0 from 0X inaccordance with the function EM(6MF[t]) In accordance with establishedconvention, i is the pure imaginary \/1 land e is the base of naturallogarithmic system.

The field intensity E(:c,t) across the mouth of radiator 5i, as afunction of the distance :c from origin O andA of time t is given by theFourier transform of (5) and is proportional to (6)VV EM(9MFUD2sfieznzsflcdg force small compared to one radian, where f is theradiation frequency and cis the velocity oflight, so that )t(Wavelength) Y Expressing this distance in terms of wavelengths by therelation il! Y l X- and letting M -.tanti so that do=da this be writteni E'tt, agfiflaftxtMFcif Emaaffrfdz (7) may In this expression, the rstfactor of the right wat@ 'sin 2m+ 1) @met 9) where i.=\/:- and .lp(r) isthe Bessel function,

of first kind and order p with argument r=21rXM, e

This may be expanded into:

anamorf tribution of electric eld intensity m across x the face' of theradiator, as given by s.: E".=J,(21rXM)`fillV E}(z)e"x=dz (1:1) Thephase of each of these` components is determined bythe real andimaginary' components of the corresponding terms of (10)'.

According to the present' invention the desired scanning of theresultant directivity pattern- E`(z)` is produced by separatelygenerating each of these side band frequency components, and thenradiating each of these components independently', with its owndirectivty characteristic, such that the' combined radiation at adistance from the radiator will produce the same eiect as' a rapidlyscanned, highly ldirecztivebeam'. In this system, al1 the directivitycharacteristics cover the saine portion of space. but with independentamplitudes in any given direction.

As a practical form of radiator, according tol this aspect of theinvention, a plurality of very narrow reflectorsv or' electrma'gnetichorns may be utilized, as shown in Fig. 1Q, each radiating a single sidefrequency. Each of these radiators 1s adjusted 'or selected inaccordance with the considerations given below so as to provide thedesired directivity characteristic corresponding to me particular sidesans component which the radiator radiates. The various side frequenciesmay be generated, as shown inthe same manner as in Fig. 7. The phases'and amplitudes of these various side frequencies may be adjusted to theValues required, in accordance with the considerations set forthabove,by use of amplitude and phase adjusters 45.

Frequency components will be practically important for values of m up toapproximately 21rXM. The maximum value XM of X will occur at the edgeof. the radiator, or for X==XM where 2a is the total radiator aperture,as shown in Fig. 9. Then where rb is the angular beam width between halfpower points. The number of side frequencies is determined by thelargest value' q' of m necessary, which will thus be given by The totalfrequency band width is of course given by zqfo'.. If the beam is to beswung rapidly, fd is large; 'givingv large band width. If the' sweepangle 2M is much larger than the pattern width la q is large, alsogiving large band width.

The manner in which a suitable scanner may be designed will now beindicated. The first information to be determined is the' character orshape of the radiationpattern desired, that is, the particular variationof electric eld intensity at a large distance from the radiator asafunction of angular orientation with respect to the radiator. In thefollowing two illustrations it will be assumed that This yields aradiation pattern having an angular width between the half-power pointsof .04 radian or slightly over two degrees, which is a practicalv'a'lue. This radiation pattern is plotted in Fig. 11, the amplitude ofEM along the axis of greatest directivity, for which 2:0, beingarbitrarily chosen as unity.

-Assuming rstly a fairly small beam swing 2M equal to one-half thepattern width or .02v

radian, the variation of the peak electric eld intensity E'M across theaperture of the radiator, which' isv essentially the Fourier transformof the spacey pattern, will be shown in Fig. 12, plotted against X,which is the distance from the focal axis OX in terms of wavelengths. Itis expressed E1ir=lt-01'14X2 ('14) It will be noted from Fig. 12 that,in the illustration used, EM is appreciable out to about 15 wavelengthsfrorn the focal axis, so that the radiator aperture should preferably be30 wavelengths or larger. At microwave wavelengths, such as of the orderof ten centimeters or less, this produces a fairly practicable size forthe radiator.

For the value of 2cm selected above, ql so that only three frequencycomponents need be considered, those for m-Y--l-l, vnr-0, and m=1, whichcorrespond to the carrier frequency f, the upper side band ,f-l-fo andthe lower side band f-fo. The amplitude of each of these components isgiven bythe quantity Jm(21rXq M), where, for the carrier component mtakes on the value zero whilenfor the first side band (either upper orlower) m takes on the value 1. (Since J-m=J+m) Fig. 13 shows the graphsof Jo, J1 and J 2 as functions of X for the value of f/M assumed in thisillustration. The product of the curve of Fig. l2 by each of the curvesof Fig. 13 gives the electric eld intensity EM required across the faceof the radiator, for the respective frequency componentsV and these areplotted in Fig. 14. The curve labeled Eo is the amplitude characteristicfor the component of carrier frequency f, while Ei is that for f-l-fo orf-fo. It will be seen that the amplitude of the second order side bandcornponent shown by curve E'z, is extremely neglig'ible, in agreementwith the analysis determining qM, and that the amplitude of the rstorder side band amounts only to approximately' 15 percent of the carrieramplitude.

The type of radiator which will produce the characteristic' of curve Eoof Fig. 14 may be determined empirically or experimentally, for example,by starting with a thin parabolic cylindrical reflector and distortingthe parabolic wall thereof. However, an actual parabola will serve as asuitable approximation in many instances.

It will be noted that the curve E1 has positive polarity for one-halfand negative polarity for the other half. This indicates that theelectric field intensity should be of opposite phase, or degrees phasedifference, in the two halves. Such a wave may be radiated by the use oftwo separate radiators, each having half the aperture of the majorradiator and excited in phase opposition. As shown in Fig. 15, twoelectromagnetic horns may be used. If desired, a single horn with acenter septum 'i2 and with its two halves independently excited in phaseopposition may be used as shown in Fig. 15A.

If desired, suitably excited reflectors could be used in place of thehorns of Figs. 15 and 15A, these reflectors being shaped and/or excitedto produce the same radiation.

Alternatively, as shown in Fig. 16, a single elecatea-281i tro-magnetichorn may be utilized which carries vanes 13 dividing it into sectors. Byadjusting the relative spacings of the sectors at the input and outputend of the horn various amplitude distributions can be obtained, asrequired.

In this way, by synthesizing singl frequency waves, each with its properspace pattern, the required scanning is obtained.

As a second illustration, let it be assumed that the same space patternE) is required to be scanned, but with a beam swing of twice thel beamwidth or .08 radian in the example chosen.V

In this instance, q is approximately 4, so that all components up to thefourth order side band will be required, namely, nine frequencycomponents in all:

, i-Jo, fi2fu, fi3fn, and f- Hifo Fig. 17 shows the the correspondingBessel functions for the rst eleven frequency components, correspondingto Bessel functions up to the fifth order, it being noted that the samefunction applies for corresponding upper and lower side band components.It will also be noted that Fig. 18 is essentially the same as Fig. 13,but with com pressed Vabscissa scale. The products of the curves of Fig.18 by Fig. 1'? gives the space dis tributlon of th-e amplitude of theelectric field intensity across the aperture of the radiator for each ofthe various side band components as shown in Fig, 19. It will be seenthat the fourth order component E4 is only substantially three percentof the carrier component E'n and can be practically neglected. The thirdorder component Ea which is about only seven percent that of the carriermay also be neglected for a rougher approximation. 'In this instance itwill be noted that the carrier component Eu also has phase reversals inthe sections separated from the axis by more than approximately tenWavelengths. These phase reversals, as indicated above, can be obtainedby separate horns or antennas, orby suitably designed sectoral horns. L,

As in the first illustration, upper and lower side band components ofthe same order have the same amplitude distributions.

These two illustrations should serve to indicate the general method ofanalysis utilized in practicing the present invention. a rapidlyscanned, inertialess directivity characteristic is provided, in whichsingle frequency Waves are radiated with particular space distributionpatterns so that at points in space removed from the radiator all of thefrequencies combine to form what is essentially a rapidly scanned,highly directive radiation pattern.

As many changes could be made in the above construction and manyapparently widely dii'- ferent embodiments of this invention could bemade Without departing from the scope thereof, it is intended that allmatter contained in the above description or shown in the'accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

What is claimed is:

l. The method of scanning a directional radiant energy beam comprisingthe .steps of producing a sequence of time-displaced, pulsed highfrequency electromagnetic Waves, and radiating said Waves withrespectively diiierent directivity characteristics, said characteristicshaving diverging axes of maximum directivity and having partiallyoverlapping directivity patterns. Y

transform of the space pat-` tern of Fig. 11 for this condition. Fig. 18shows By this invention 1'4"v 2. The method as in claim 1v wherein saidwaves comprise repetitive periodic pulses of high frequency energy, eachof said pulses having a rounded envelope.

3. The method as in claim l wherein each of said waves comprises aperiodicsequence of pulses of high frequency electromagnetic energy,-each of said pulses having an envelope of the shape of a cosine-squaredWave, and the pulses of successive time-displaced waves being timedisplaced by an amount substantially equal to half the total pulseduration, whereby said suc cessive wave pulses are partially concurrent.

4. The method O-f scanning a highly directional high frequencyelectromagnetic wave comprising the steps of producing a plurality ofequally spaced single frequency waves, adjusting the amplitude of eachoi' said Waves to c-orrespond to the amplitude of a side band frequencycomponent of a pulsed high frequency electromagnetic wave, combiningsaid amplitude adjusted Waves to produce 'a first combined wave, phaseshifting said adjusted waves by equal amounts corresponding to thefrequency of said waves to form further combined waves, the phasevcharacteristics having diverging axes of maniu mum directivity andbeing partially overlapping.

5. The method of scanning a directional radiant energy receptivitypattern comprising receiving said energy simultaneously with a pluwrality of different receptivity characteristics having differing axes ofmaximum receptivity, and selectively and successively transferring saidreceived energy to a utilization circuit, the periods of saidtransference being partially concurrentJ for successively transferredenergies.

6, The method of scanning a directional radiant energy beam comprisingthe steps of producing a plurality of single frequency each successivepair of waves having equal frequency difference, and independentlyradiating each of said waves into a :common predetern mined portion ofspace, and with an individual directivity characteristic, saidcharacteristic being determined by the corresponding Fourier componentof the Fourier transform of the de sired scanned pattern at distancesremote from said radiator.

7. The method of scanning a directional elcctromagnetic energy beamcomprising the steps s of producing a plurality of single frequencyWaves, and independently radiating each of said Waves into the samepredetermined portion of space with an individual directivitycharacteristic 'chosen to provide a combined electromag netic'field atpoints distant from said radiation of a character equivalent to scanningof a directional beam.

8. High frequency radiant energy scanning apparatus comprising means forproducing a sequence of time-displaced pulsed high frequency lelectromagnetic waves, a corresponding pluraiity of antennae meanshaving respectively different directivity characteristics withdii/'erging axes ci' maximum directivity and `partially overlappingdirectivity. patterns, and means for exciting each` of said antenna by acorresponding one 'of said waves.

9. High prising means for producing a plurality of high frequency Waves,each having a periodic sequence frequency scanning apparatus com` ofpulses oihigh frequency electromagnetic' energy, each of said pulseshaving a, rounded envelope and the pulsesof successive time-displacedlwaves being time-displaced by an` amount substantially equal to half thetotal pulse duration, whereby said successive wave pulses are partiallyconcurrent, a corresponding plurality of directional antennae havingdiverging axes-of maximum directivity and partially overlappingdirectivity patterns, and means for exciting, each of said antennae by acorresponding one ofsaid WaVeS.

10. High frequency apparatus comprising aplurality of directionalantennae having respectively diverging and overlapping.` directivitycharacteristics, means for producing a corresponding plurality ofpulsed, time-displacedhighv frequency waves and means for exciting said-antennae respectively by said waves.

11. Apparatus as in claim 10 wherein said pulsed waves are partiallyconcurrent.

12. Apparatus as in claim 10 whereinthe envelope of said pulsed waveshas a rounded form and is partially concurrent.

13. High frequency apparatus comprising a plurality of circuits adaptedeach to operate at a single frequency, said plurality of frequenciesbeing equally separated, a plurality of phase Shifters connected to eachof said circuits in cascade, the phase shifters connected to any onecircuit having equal phase shifts at the corresponding frequency of saidone circuit, the phase shiftersconnected to different frequencycircuits-A having phase shifts linearly related to the frequency of therespective coupled circuits.

14. High frequency scanner apparatus comprising a plurality ofcircuits'each adapted to operate at a single frequency, said singlefrequencies being equally separated, a plurality of directional antennaehaving diverging axes of maximum directivity and partially overlappingdirectivity characteristics, and means coupling each of said antennaewith all of said circuits,

each said coupling means comprising a set of phase shifters coupledrespectively to sai-dy circuits and producing respectiveY phase' shiftslinearly related to the respective frequencies of said circuits coupledthereto, the phase shifters of the respective sets coupled to the samecircuit having integrally related phase shifts.

l5. High frequency scanner apparatusy com prising a plurality ofcircuits each adapted to operate at a single frequency, said singlefrequencies being equally separated, a plurality of directional antennaehaving diverging axes of maximum directivity and partially overlappingdirectivity characteristics, and means for coupling each said antennaewith all said circuits with respective phase shifts linearly' relatedto' the frequency of said circuits, the resulting sets of phase shiftsfor' said antennae being proportional.

16. High frequency apparatus for producing a plurality of time-displacedmodulated high frequency waves, comprising a plurality of sources ofhigh frequency wave having equally separated frequencies, said sourcebeing arranged in pairs equally separated in frequency above and belowthe frequency of a predetermined source, a plurality of phase-shiftingconductors havingv equal phase shift per unit length and arranged' inconcentric semi-circles with radii proportional to successive integers,means connecting each pair of said sources to the ends of al respectivesemi'- circular conductor, and a plurality of outputcon'- 16 ductormeans coupled to radially disposed points of said semi-circularconductors, whereby the combined waves supplied t0 said output conductormeans are similarly-modulated but timedisplaced waves thetime-displacement between any two waves being proportional to the anglebetween the radial arrangements of coupling points for said two waves.

17. High frequency scanning apparatus comprising means for producing aplurality of equally spaced single frequency waves, means for adjustingthe amplitude of each of said waves to correspend to the amplitude of aside band frequency component of a pulsed high frequency electromagneticwave, means for combining said amplitude-adjusted waves to produce afirst combined wave, means for producing further waves which aresuccessively time-displaced versions of said first combined wave, aplurality of directional antennae having diverging axes of maximumdirectivity and with partially overlapping directivity patterns, andmeans for exciting each of said antennae by a corresponding one of saidcombined and time-displaced Waves.

18. High frequency scanning apparatus for scanning a predetermined spaceradiation pattern over a predetermined angular swing, comprising aplurality of sources' of single high frequency waves having equalfrequency difference, and a corresponding plurality of apertureddirective antennae coupled respectively to said sources and havingrespectively different substantially overlapping directivitycharacteristics, each of said antennae having an electric fieldintensity varying across the aperture thereof as a function of distancefrom the center of said'aperture, in accordance with the product of theFourier transform of said predetermined pattern times a Bessel functionof argument proportional to said distance and to said angular swing andof order equal to the value of the frequency separation of the frequencyof the source corresponding to said each antennae from the middlefrequency of said sources divided by said frequency difference.

19. High frequency scanning apparatus comprising means for producing aplurality of equally separated single frequency waves, a correspondingplurality of directional antennae having substantially overlapping anddifferent directivity characteristics, and means for exciting each ofsaid antennae by a respective one of said waves, said directivitycharacteristics being chosen to provide a combined electromagnetic eldat points distant from said antennae of a character equivalent toscanning of a directional radiant energy beam.

20; Apparatus as in claim 19 wherein each of said directivitycharacteristics corresponds to a Fourier component of the Fouriertransform of a desired directivity pattern to be scanned.

21. High frequency scanning apparatus for scanning a predetermined spaceradiation pattern, comprising a plurality of sources of single highfrequency waves having equal frequency difference, and a correspondingplurality of apertured directional antennae coupled respectively to saidsources and having respectively different substantially overlappingdirectivity characteristics, each of said antennae having an electriceld intensity varying across the aperture thereof in accordance with theFourier transform of said predetermined pattern.

22. High frequency scanning scanning a predetermined space apparatus forradiation pat- 17 tern over a predetermined angular swing, comprising aplurality of sources of single high frequencv waves having equalfrequency difference. and a corresponding plurality of apertureddirective antennae coupled respectively to said sources and havingrespectively different substantially overlapping directivitycharacteristics, each of said antenna having an electric field intensityvarying across the aperture thereof as a function of distance from thecenter of said aperture in accordance with a Bessel function of argumentproportional to said distance and to said angular swing.

GEREID LEON TAWNEY.

Certificate of Correction `Patent No. 2,437,281: March 9, 1948.

GERELD LEON TAWN EY It is hereby certied that error appears in therinted specification of the above numbered patent requiring correctionas follows: olumn 6, line 43, for the word upon read upper; and that thesaid Letters Patent should be read with this correction therein that thesame may conform to the record of the case in the Patent Office.

Signed and sealed this 25th day of May, A. D. 1948.

.THOMAS Fr MURPHY,

Assistant Uommsszoner of Patents.

. Y HIGH FREQUENCY RADIANT TUS. Patent dated Mar. 9, 1948. Disclaimerfiled Sept. 14, 1949, by e assigne Ww Sperry Corporation. ereby entersthis disclaimer to Certificate of Correction Patent No. 2,437,281: March9, 1948.

GERELD LEON TAWNEY It is hereby certied that error appears in theprinted specification of the above numbered patent requiring correctionas follows: Column 6, line 43, for the Word upon read upper; and thatthe said Letters Patent should be read with this correction therein thatthe same may conform to the record of the case in the Patent Oflice.

Signed and sealed this 25th day of May, A. D. 1948.

[IML] THOMAS F. MURPHY,

Assistant Uommesz'oner of Patents.

